The present invention relates to a method and an apparatus for forecasting forthcoming shadowing of a photovoltaic system connected to a power grid due to cloud formation or cloud movement.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Supply contracts with associated energy providers frequently require that the solar power plants are designed to supply to the power grid an agreed-upon minimum power within a determined time interval. For example, a 2.4 MW solar power plant may be required to supply between 11 AM and 5 PM at least 60% of the rated power, meaning about 1.5 MW. Depending on the weather, this minimum power cannot always be generated by the solar system alone. Backup power plants supplying DC current, for example a battery or a fuel-cell, must be switched in. For a longer forecast decrease in energy, an additional power plant must be commissioned on the AC side. This is implemented either by purchasing the required energy from another energy supplier by adding an additional power plant on the AC current side, for example in form of a diesel generator or a gas power plant. The respective energy suppliers have different startup times until the energy can be supplied. This ranges from the almost immediate discharge of a battery to approximately 5 minutes for starting out an additional power plant.
The decision, which measures are potentially the most appropriate, depends to a large degree from the incident sunlight to be expected on the area of the photovoltaic system. The energy supplier is generally interested in being informed about an impending decrease in the available energy. This can be addressed, for example, by early disconnection of users from the grid, whereby their operation can then be resumed at a later time. Such approach is indicated, for example, in the production of hydrogen.
It would therefore be desirable and advantageous to provide a method and an apparatus for identifying a impending undersupply and to rank its expected duration and severity, so that a selection can be made, which additional energy supplier should be prepared and provisioned for supplying the energy, so that the desired minimum power can be called up at any time, or that alternatively the disconnection of users from the grid can be initiated.